Apparatus for thermographic duplication of a radiation absorbent picture

ABSTRACT

An apparatus for thermographic series-duplication of an original bearing heat radiation-absorbent indicia comprises a rotary drum having means for mounting the original on a first imprint of the external surface thereof, at least one source of infrared radiation mounted outside the drum for successively irradiating the original during the rotation of the drum, a first roller for pressing a web coated with a fusible dye into temporary contact with the original subsequent to its irradiation to cause the original to pick up dye from the web in accordance with its heated indicia pattern, and a second roller for pressing a copy sheet into temporary contact with the original subsequent to its contact with the coated web to cause the copy sheet to pick up an impront of the dye image from the original, the drum being adapted to start and stop in a predetermined angular position in which said source of infrared radiation with irradiate a second part of the external surface of the drum which is spaced from said first part thereof in a manner to prevent excessive heat transfer between the two parts.

United States Patent Kvarnegzird [54] APPARATUS FOR THERMOGRAPI-IIC DUPLICATION OF A RADIATION ABSORBENT PICTURE [72] inventor: Sven Bertil Kvarnegard, Enebyberg,

Sweden [73] Assignee: Alttiebolaget Carl Lamm, Stockholm,

Sweden [22] Filed: Mar. 4, 1969 [21] Appl.No.: 804,073

[30] Foreign Application Priority Data Mar. 20, 1968 Sweden ..3726/68 [52] [1.8. Ci. ..250/65 [5 l] ..B41m 5/002 [58] Field of Search ..250/65.l

[56] References Cited UNITED STATES PATENTS 3,414,724 12/1968 Kvamegard ..250/65.1

[451 Apr. 4, 1972 Primary Examiner-James W. Lawrence Assistant Examiner-C. E. Church Attorney-Arnold Robinson [57] ABSTRACT An apparatus for thermographic series-duplication of an original bearing heat radiation-absorbent indicia comprises a rotary drum having means for mounting the original on a first imprint of the external surface thereof, at least one source of infrared radiation mounted outside the drum for successively irradiating the original during the rotation of the drum, a first roller for pressing a web coated with a fusible dye into temporary contact with the original subsequent to its irradiation to cause the original to pick up dye from the web in accordance 12 Claims, 1 Drawing Figure APPARATUS FOR THERMOGRAPHIC DUPLICATION OF A RADIATION ABSORBENT PICTURE This invention relates to thermographic series-duplication on unprepared copy receiving sheets of a radiation absorbent picture appearing on an original having in itself a comparatively small tendency to absorb radiated heat, while utilizing the original as an intermediate means for transferring selected spots of a dye composition, which is substantially non-smeary at room temperature but is fusible into a transferable state by heating, from a carrier of a coating of said composition to each copy receiving sheet.

More particularly the invention is concerned with an apparatus for carrying out such series-duplication and being of the kind comprising, in combination, a rotary drum, which is adapted to carry the original on a part of its envelope surface during the duplicating process and to always start and stop its rotary motion in a substantially predetermined angular position, at least one radiation source unit having a high intensity, particularly within the infrared radiation range, which unit is adapted to form at least one radiation zone extending axially along the drum and having a limited extension in the circumferential direction thereof, through which zone the original will be passed during the rotation of the drum so that the radiation absorbent picture on the original will assume a higher temperature than the surrounding, means for bringing a web-like carrier of a coating of a fusible dye composition into intimate contact with the original in order to effect a transfer of dye spots to the latter in accordance with the heated picture thereon, said means including a conducting roller adapted to be pressed towards the drum and having the web-like dye composition carrier running over it towards the original, and means for subsequently transferring from the original to a copy receiving sheet at least a substantial part of said dye spots previously transferred from the dye coated carrier to the original, said means comprising a pressure roller operative to bring the copy receiving sheet into intimate contact with the original carried by the drum.

A previously known apparatus of this kind is described in the U.S. Pat. No. 3,414,724. In this known apparatus the radiation source unit is arranged inside a drum, which for its major part is made of transparent glass material. This, however, gives rise to many technical problems not only from a constructional but also from a functional point of view. Already the arrangement of stationary components inside the rotary drum is technically complicated, and to this comes the difficulties in removing from the interior of the drum all the excessive and objectionable heat deriving from the powerful radiation source unit, in particular when the apparatus is intensely utilized and forced to operate at a high copying speed. Furthermore, it is inevitable in the known apparatus that a certain part of the radiation power is lost in the transparent envelope wall of the drum and that the special requirements as to the nature of the original may sometimes be embarrassing.

In this specification and in the accompanying claims the term original should be understood not only as any kind of sheet-like bearer of a heat radiation absorbent picture to be copied, but also such a bearer in combination with any suitable covering sheets or films capable of adapting the same for the reproduction in one respect or another and accompanying the bearer during the duplication process in the apparatus. By way of example, such a covering may consist of non-transparent concealing slips or sheets of a material having a low radiation absorption capacity, which may be blank to merely prevent copying of certain picture parts or be provided with text or pictures to complete the original. Also a covering may consist of a thin, transparent film, which is capable of improving the surface character and the dye-transferring properties of the picture bearer or simply has to protect the picture bearer itself from direct contact with the dye. In connection with this invention the picture bearer can be either transparent or at least translucent, and if so it is of no importance on which side thereof the radiation absorbent picture is provided, or it may be non-transparent, in which case the radiation absorbent picture must be a mirror picture on the side of the bearer facing away from the drum during the duplicating process.

The main features of the apparatus according to the invention are that the radiation source unit is arranged outside a drum having its envelope surface circumferentially divided into a first part serving as a support for the original, and a second part separate from said first part and arranged so as to take a position in front of the radiation source unit, when the drum is at standstill in its predetermined start and stop position, the said second part of the envelope surface of the drum being adapted to receive concentrated heat radiation without transmitting any considerable amount of heat to said first surface part supporting the original, and that the conducting roller for the web-like dye composition carrier is arranged to move the latter into contact with the original first at a point located after the radiation zone produced by the radiation source unit, as viewed in the direction of rotation of the drum, so that irradiation of the dye composition carrier during its contact with the original is avoided, the conducting roller being arranged so as to be pressed towards the drum only when said first surface part thereof supporting the original is passing by, and to be departed from the drum during the passage of the second surface part of the drum.

In this manner the aforesaid disadvantages of the known apparatus are eliminated and considerable improvements achieved, in particular as far as the efficient cooling of the apparatus and the protection of the dye composition carrier from excessive heat is concerned. The fact that the radiation source unit always requires a certain time for reaching its full radiation power and always continues to deliver a certain remnant radiation, even after the current supply thereto has been broken, does no longer cause any considerable trouble. Furthermore, the delayed contact between the irradiated original and the dye composition carrier allows, at least in certain forms of the apparatus embodying the invention, the use of a dye composition, which is considerably more radiation absorbent and thus rendering an easier-to-read copy imprint than has previously been possible in the so-called thermographic fusible dye process, and this thanks to the fact that the dye composition carrier need neither be irradiated nor through-radiated during the copying process.

In a preferred form of the apparatus according to the invention the first surface part of the drum serving as a support for the original is heat insulating in' itself, i.e., is made of heat-insulating material, or provided with a heat-insulating surface covering, e.g., in the form of a fine-meshed polyamide fiber fabric. In both cases it has also been found advantageous to provide the drum part with a heat repellent surface coating, such as by gilding. In this way a heat transfer in both directions between the radiation absorbent picture on the original and the drum, which could cause blur especially in rapid production of large series of copies from one and the same original, is successfully prevented. The second part of the envelope surface of the drum is suitably made of a heat resistant material and has, preferably, radiation reflecting surface properties in order to minimize heating thereof, when it is subjected to the radiant heat from the radiation source unit.

Since the conducting roller for the dye composition carrier is arranged to be alternately pressed towards the drum and departed therefrom, it has been found advisable to put the dye composition carrier in motion over the conducting roller before the latter is pressed towards the drum. In this manner possible slip between the dye composition carrier and the original is successfully avoided, which in turn will improve the transfer of dye to the original mounted on the drum. In a particularly advantageous form of apparatus embodying the invention the dye composition carrier is arranged, when running over the conducting roller, to be transferred between two spools incorporated together with the conducting roller in a detachable, symmetrical and reversible magazine unit in the apparatus. This will make possible a convenient and full use of dye composition carriers in the form of factory-coated thin webs, which, by reversing the magazine unit at suitable intervals, can be fed several times back and forth through the apparatus before the dye composition coating thereon is completely consumed. When the magazine unit is being inserted in the apparatus, the spools are preferably connected with each one slip coupling, the one of which is transmitting a driving power and the other a braking power to the dye composition carrier in order to start the feeding thereof prior to the pressing of the conducting roller towards the drum and to accomplish appropriate retardation of the carrier web to avoid uncontrolled movements thereof. Preferably the first one of said slip couplings is then adapted to start driving of the dye composition carrier first when the conducting roller comes within a predetermined distance from the drum, and to cease driving it as soon as said distance is exceeded during the departure of the conducting roller from the drum, the said coupling being also adapted to slip as long as the conducting roller holds the dye composition carrier in such an intimate contact with the original carried by the drum that the friction between the original and the dye composition carrier will govern the feed of the latter over the conducting roller.

In a preferred form of the apparatus embodying the invention the means for transferring the dye composition from the original to the copy receiving sheet includes, in addition to the previously mentioned pressure roller, also a second radiation source unit, which, like the first mentioned one, is operative to subject the original carried by the drum to a high intensity infrared radiation within a second radiation zone that is axially extended but circumferentially restricted relative to the drum, and this before the original is brought into contact with the copy receiving sheet to give away its dye spots to the latter. The additional features of this form of the apparatus are that also the second radiation source unit is mounted outside the drum and in such a manner that it will irradiate the original immediately before it arrives to the pressure roller and comes into contact with the copy receiving sheet, and that also this second radiation source unit is so positioned in the apparatus that it will irradiate the aforesaid second surface part of the drum in the start and stop position of the latter. In this way the same advantages are achieved with respect to the arrangement of the second radiation source unit as have already been stated in connection with the first radiation source unit. Preferably, the second radiation source unit is arranged to irradiate the original in obliquely forward direction, as compared with the direction of rotation of the drum, so that the renewed heating of the radiation absorbent picture on the original will take place immediately prior to the contact between the original and the copy receiving sheet and, hence, without appreciable heat loss to the surroundings.

Like the conducting roller for the dye composition carrier the pressure roller for the copy receiving sheets is, preferably, arranged to be pressed towards the drum only when the first surface part of the drum supporting the original is passing by, and to be departed from the drum when the second surface part of the drum is passing the same during each revolution of the drum. This will prevent possible heat damage to the pressure roller, which is normally made of rubber and on the roundness and smooth although relatively hard surface of which the quality of the copies is highly depending.

In order to give the apparatus an appropriate and attractive design, when a second radiation source unit is provided therein, it has been found advantageous to locate said unit and the pressure roller in such a manner within the apparatus that the original, when the drum is started, will have to pass the same before reaching the first radiation source unit and the conducting roller for the dye composition carrier, both radiation source units then being arranged on the underside of the drum. Although with such an arrangement of parts the very first copy of an original can only be produced during the second revolution of the drum, this is of no importance, since the apparatus embodying the invention is primarily intended to produce large series of copies from each original. It is obviously more important that the apparatus can be so built that it is expedient to work with and that such operations as the attachment of the original to the drum, the feeding in of the copy receiving sheet, the exchange of the dye composition carrier, and the reversal of the magazine unit, if provided, are facilitated as much as ever possible.

For further elucidation of the invention an embodiment thereof will now be described with reference to the accompanying drawing which shows a partly diagrammatical longitudinal sectional elevation of a preferred form of the apparatus, it being taken for granted that the man skilled in the art will readily understand that the apparatus must also include at least one driving motor and necessary transmissions for the various driven components. It should also be readily understood that various modifications with respect to the details of the illustrated apparatus are thinkable without affecting the aforeseen operation thereof described in the following.

The apparatus shown in the drawing comprises in the first hand a suitable, combined casing and supporting structure, generally designated by numeral 1, in which there is rotatably journalled a cylindrical drum, generally designated by 2. In a manner not shown but well known in the related art, the drum 2 is driven by an electric motor through a clutch coupling, which causes the same to always start and stop its rotary motion, which may include one single or several continuous revolutions, in a substantially predetermined angular position, viz, that which is shown in the drawing. The envelope surface of the drum 2 is circumferentially divided and comprises a first part 2A corresponding in length to approximately three quarters of the total circumference of the drum. This first surface part 2A is intended to serve, at least partially, as a support for an original 3, and to permit mounting of the latter the drum is provided with suitable, releasable clamping means 4 for the foremost marginal portion of the original. The surface part 2A of the drum may be made either of a material having in itself poor heat conducting properties or of metal, and in the latter case it should be provided on its outside with a heat insulating surface covering 5, at least under the original 3. In both cases it has been found very advantageous to make the surface part 2A heat repellent, such as by gilding. The heat insulating surface covering 5 can to advantage consist of a fine-meshed polyamide fibre fabric. The remaining, second part 2B of the envelope surface of the drum is suitably made of a heat resistant material and provided with a heat radiation reflecting coating, e.g., of a blossy metal. In order to minimize the heat transmission between the envelope surface parts 2B and 2A as far as possible, they may be separated by air gaps 6 or heat insulating material. The drum 2 is also provided with end walls 7, only one of which is visible in the drawing, and each of them is on its outside provided with a curved groove forming an endless guide 8, the purpose of which will appear from the following. The arrow A indicates the direction of rotation of the drum.

For effecting the transfer of fusible dye composition to selected spots on the original 3 carried by the drum, the apparatus is provided with a first, elongate heat radiation source in the form of a tubular infrared radiator 9, which is electrically energized through conductors and switches not shown in the drawing. The infrared radiator tube 9 extends parallely to the drum 2 substantially along the entire length thereof and is combined with a suitable reflector 10 of substantially semi-elliptic cross section. The tube 9 is stationary mounted outside the drum 2 and located in the one focus of the reflector 10, the other focus of which substantially coincides with the outer envelope surface of the drum 2 in such a manner that the radiation source unit 9,10 will create a concentrated radiation zone 11 extending axially relative to the drum and having a very restricted width as viewed in the circumferential direction of the drum. This radiation zone 11 will be passed by the original 3 during the rotation of the drum and the concentrated heat radiation will then cause the radiation absorbent picture on the original to assume a higher temperature than the surroundings. In the start and stop position of the drum the radiation zone 11 will, however, be in front of the second surface part 2B of the drum, as shown.

The means for transferring dye composition to the original 3 also include a web-like dye composition carrier 12 running over a conducting roller 13, which is parallel to the drum 2 and adopted to be pressed towards the latter at a point located a short distance behind or after the radiation zone 11, as viewed in the direction of rotation of the drum and as indicated by dash-and-dot lines in the drawing. The conducting roller 13 is a freely rotatable roller having, preferably, a relatively soft, elastic surface, and it forms part of a detachable, symmetric and reversible magazine unit, generally designated by 14, which also comprises, besides substantially triangular end pieces 15, two spools 16 and 17, between which the dye composition carrier web 12 is running. Preferably, the web 12 consists of a very thin sheet of paper, which on its side facing outwards at the passage over the conducting roller is coated with a thin layer of thermographic dye composition and which generally resembles a usual carbon paper. The spools 16 and 17 are made sufficiently large to take up a considerable length of such a web 12, which is most commonly factory-coated and the width of which usually is substantially the same as the axial length of the drum 2. The magazine unit 14 is detachably and reversibly mounted in a cradle 18, which is swingable about an axis represented by pivot 19 in the drawing and extending parallely to the drum and to the conducting roller 13. The cradle 18 is provided with an arm 18 at each end of the drum 2 and each such arm has a guide pin 20, which cooperates with the groove 8 provided in the respective end walls of the drum, and this in such a manner that, when the drum is rotated, the cradle 18 together with the magazine unit 14 is brought to alternately swing in the clockwise and the counterclockwise direction about the pivot 19. Accordingly the conducting roller 13 is brought to move towards and away from the drum, respectively, in a manner to bring the dye composition carrier web 12 into contact with the original 3 mounted on the drum 2, but also to remove it from contact with the drum at least when the surface part 2B thereof is passing the conducting roller. The position of the reversible magazine unit 14 relative to the cradle 18 is determined partly through co-operation between the shaft ends of the conducting roller 13 and open bearings, not shown, which are adjustably mounted on the cradle 18 by means of brackets 21, partly through a hooking engagement between pins 22 on the end pieces of the magazine unit and corresponding incuts 23 in the end walls of the cradle 18.

The drum 2 is supposed to be rotated at a relatively high speed, when the apparatus is in use. Therefore it has been found advantageous to start moving or feeding the dye composition carrier web 12 over the conducting roller 13 already somewhat before the web comes into contact with the relatively rapidly passing original 3. It has also proved desirable to subject the web 12 to a certain braking in order to keep it running smoothly and regularly between the spools 16 and 17 of the magazine unit. To this end the two spools are arranged so as to become connected with each one slip coupling 24 and 25, respectively, when the magazine unit 14 is mounted in the cradle 18. In this arrangement the one slip coupling 24 is adapted to transmit a moderate braking power to the lower, unwinding spool 16, while the other slip coupling 25 is adapted to transmit, from a power transmission system not shown, a moderate driving power, likewise of a very moderate magnitude, to the upper spool 17, the coupling 25 being also adjusted to slip as soon as the dye composition carrier web 12 comes into contact with the original 3 carried by the drum 2, so that in the latter case the speed of the original itself will govern the feeding speed of the web over the conducting roller 13. Furthermore, driving power is, in a manner well known per se, only selectively transmitted to the coupling 25 in response to the angular position of the cradle 18, so that driving of the web is effected only as long as the conducting roller 13 is within a predetermined distance from the drum 2, the power transmission being interrupted as soon as this distance is exceeded during the departure of the conducting roller from the drum. In this way a continuous feeding of the dye composition carrier web is avoided, which will improve the possibilities for a full consumption of the dye composition layer on the web, before the latter has to be replaced by a new one.

The copy receiving sheets C are placed on a table 30 provided in the left-hand part of the apparatus, from where they are fed in, one by one, either manually or by means-of some well-known feeding mechanism, not shown, in the direction of the arrow 31 between a pair of rollers 32 and 33, respectively, at least one of which is driven, so that the said rollers will forward each copy receiving sheet between suitable guiding means 34 to the interspace between a pressure roller 35 and the drum 2. The pressure roller 35 is movable towards and away from the drum and more specifically it is rotary mounted between two bell crank levers 36, each of which is swingable about a pivot 37 and has an extended arm 36 carrying at its outer end a pin or roller 38 co-operating with the previously mentioned curved groove or guide 8 in each end wall 7 of the drum 2. The pressure roller 35 has a relatively hard rubber surface and presses, when swung in towards the drum 2, the copy receiving sheet into contact with the passing original 3. A short distance behind or after the pressure roller 35, as viewed in the direction of rotation of the drum 2, the copy receiving sheet is then again removed from contact with the original 3 by means of a knife-like member 39 and pushed away between this member and a guide plate 40 to a collecting box 41 or the like, as generally indicated by the arrows 42. Of course, the collecting box 41 can be replaced by a conveyor, a chute or the like, by means of which the produced copies can be discharged on any suitable side of the apparatus.

Immediately before or in front of the place where, during the rotation of the drum, the pressure roller 35 brings the copy a receiving sheet into contact with the original 3 carried by the drum 2, there is arranged a second tubular infrared radiation source 43. The radiator tube 43 co-operates with a reflector 44, which can be somewhat larger than the reflector 10, and which is so positioned that the concentrated radiation from the tube 43 will be directed towards the original in an obliquely forward direction, as viewed in the direction of rotation of the drum. This has been indicated by dash and dot lines in the drawing.

As will be readily understood, the original 3 will, when passing the second radiation source unit 43, 44, be subjected to a second intense and concentrated heat radiation, so that the radiation absorbent picture thereon will again assume an increased temperature immediately before the copy receiving sheet comes into contact with the original. Also the second radiation source unit 43, 44 is arranged outside the drum 2 and in such a position that it will irradiate the second surface part 2B of the drum, when the latter is in its start and stop position, as illustrated. A suitable blower 45 provides for cooling of the reflector 44, so that secondary heat therefrom does not damage the feeding roller 32 and the pressure roller 35, and so that also the drum 2 is always kept as cool as possible. A second blower 46 is provided in the upper part of the apparatus between the drum 2 and the magazine unit 14 to blow cooling air down past and around the first radiation source unit 9,10.

When the apparatus is to be used, a sufficient length of dye composition carrier web 12 must, of course, be available on the lower spool 16 of the magazine unit. The original 3 is mounted on the drum 2 by means of the clamps 4, as shown, and the necessary copy receiving sheets C are placed on the table 30 in the apparatus. Then the apparatus is ready to be started, which means that current is supplied to the fans 45 and 46 and to the driving motor, not shown. Preferably the said motor is, in a manner well known per se, arranged to drive the necessary transmissions of the apparatus through an electro-magnetic clutch, not shown. The drum 2 is still in its start and stop position as illustrated, which also means that the conducting roller 13 for the dye composition carrier web 12 as well as the pressure roller 35 are departed from the drum. Now a suitable release button is actuated, whereby current is supplied to the two infrared radiator tubes 9 and 43 and, with a certain delay, also to the electro-magnetic clutch, so that the drum 2 will start to rotate in the direction of the arrow A. The said delay is so selected that the radiator tubes 9 and 43 have had sufficient time to reach their maximum radiation power, before the drum starts to rotate.

There is no need of feeding a copy receiving sheet into the apparatus during the first revolution of the drum, if the original has not been used in a thermographic fusible dye duplicating process before and, consequently, has no spots of dye composition on it. During the first revolution of the drum the original 3 will first pass the radiation source unit 43, 44 and then the radiation source unit 9,10 whereby its radiation absorbent picture will assume a higher temperature than that of the surrounding. At the same time, the guides 8 on the end walls 7 of the drum 2 will provide for that first the pressure roller 35 and then also the conducting roller 13 for the dye composition carrier web are pressed towards the drum, as soon as the second surface part 2B of the drum has passed. As a result of this, the dye composition carrier web 12, which in the manner already explained has been started to run over the conducting roller 13 as soon as the latter has come sufficiently close to the drum, will transfer dye composition to the original 3 in accordance with the heated picture thereon. When the drum 2 has returned to its original position after the accomplishment of a full first revolution, the current supply to the radiator tubes and the electro-magnetic clutch is interrupted, preferably automatically, and now the apparatus is ready for copying the original in practically unlimited series, a new copy receiving sheet being, of course, required at each subsequent revolution of the drum.

Each time the release button of the apparatus is now actuated, the previously described cycle will be repeated with the difference that the spots of dye composition now present on the original will become resoftened, when passing the second radiation source unit 43,44 and transferred to the copy receiving sheet, when passing the pressure roller. The dye composition spots on the original, which are thus consumed, are then immediately replenished, when the original again passes the radiation source unit 9,10 and comes into contact with the dye composition carrier web 12. If desired, the drum can, of course, rotate continuously when a large series of copies from one and the same original is produced and in such a case the radiation source units may also remain energized during the entire production time. However, the conducting roller 13 for the dye composition carrier web 12 as well as the pressure roller 35 will always move towards and away fro m the drum in the previously described manner at each revolution of the drum. When the available length of dye composition carrier web 12 has been transferred from the spool 16 to the spool 17, the operation of the apparatus must be interrupted and the magazine unit 14 be reversed. Of course, the dye composition carrier web must also be replaced by a fresh one, when the dye composition coating thereon has been entirely consumed.

It should be kept in mind that the drawing is only diagrammatical and that the shape, size and arrangement of the various components of the illustrated apparatus may be changed in several respects without affecting the operation thereof. Consequently, the example shown must not be considered to confine the scope of the following claims.

I claim:

1. An apparatus for thermographic duplication of a heat radiation absorbent picture on an original, which in itself has a negligible tendency to absorb radiated heat, while utilizing the original as an intermediate means for transferring, from a carrier of a coating of a fusible copy printing dye composition, selected spots of said composition to each of a number of copy receiving sheets, said apparatus comprising, in combination, a rotary drum arranged to start and stop rotating in a substantially predetermined angular position and having an external envelope wall divided into a first circumferentially extending surface part (2A) adapted to serve as a support for the original and having means for detachable mounting the same thereon, and a second circumferentially extending surface part (28) separated from said first surface part in a manner to substantially prevent the transmission of heat thereto, when said second surface part is subjected to heat radiation; a radiation source unit (9,10) capable of delivering a concentrated radiation rich in infrared rays towards the drum, said unit being mounted outside the drum in a manner to irradiate said second surface part thereof, when the drum is at standstill in its start and stop position, and to form a radiation zone of high intensity and limited width extending axially along the drum so as to be passed by the original with the radiation absorbent picture thereon, when the drum is rotated; a movable web-like carrier of a thin coating of the fusible dye composition; conducting means for temporarily bringing said carrier web into intimate contact with the drum-mounted original at a location behind the radiation zone formed by said radiation source unit, as viewed in the direction of rotation of the drum, and including a conducting roller arranged to be alternately moved towards the drum, when first surface part thereof carrying the original is passing, and away from the drum, when said second surface part thereof is passing; and feeding means for bringing copy receiving sheets into intimate contact with said drummounted original at a location behind that, where said conducting roller is located, as viewed in the direction of rotation of the drum, said feeding means including a pressure roller adapted to press each copy receiving sheet against the original and means for separating each such sheet with the copy imprint thereon from the drum-mounted original before the latter is again caused to pass the radiation zone formed by said radiation source unit.

2. An apparatus according to claim 1, wherein said first surface part (2A) of the drum is formed on a wall portion thereof having heat insulating properties.

3. An apparatus according to claim 1, wherein said first surface part of the drum has a heat insulating covering, at least under the original.

4. An apparatus according to claim 1, wherein said first surface part of the drum has heat repellent properties.

5. An apparatus according to claim 1, wherein said second surface part 2B) of the drum has radiation reflecting properties.

6. An apparatus according to claim 1, wherein said coated carrier web is arranged to start running over said conducting roller already before coming into contact with the drummounted original, when said conducting roller is moved towards the drum, and to cease running, when said conducting roller is moved away from the drum.

7. An apparatus according to claim 1, wherein said coated carrier web is transferred between two spools when running over said conducting roller, said spools being incorporated together with the conducting roller in a detachable, reversible and substantially symmetrical magazine unit forming part of the apparatus.

8. An apparatus according to claim 7, wherein said spools included in the detachable magazine unit are arranged, when said unit is being inserted, to be connected with each one of two slip friction clutches, the one of which is adapted to transmit a braking power and the other one a driving power to their related spools and hence to the coated carrier web running between them.

9. An apparatus according to claim 1, wherein said pressure roller forming part of the feeding means for the copy receiving sheets is arranged to be pressed towards the drum only when said first surface part thereof is passing, and to be departed from the drum at least when said second surface part thereof is passing.

10. An apparatus according to claim 1, wherein a second radiation source unit (43,44) capable of delivering a concentrated radiation rich in infrared rays is mounted outside the drum in a manner to irridiate said second surface part thereof, when the drum is at standstill in its start and stop position, and to form a second radiation zone of high intensity and limited width extending axially along the drum at a location to be passed by the drum-mounted original shortly before the latter arrives to said pressure roller, where it is brought into contact with the copy receiving sheet.

11. An apparatus according to claim 10, wherein said second radiation source unit is arranged to irradiate the passing original in an obliquely forward direction, as viewed in the direction of rotation of the drum.

12. An apparatus according to claim 10, wherein said second radiation source unit and said pressure roller forming part of the feeding means for the copy receiving sheets are so 

1. An apparatus for thermographic duplication of a heat radiation absorbent picture on an original, which in itself has a negligible tendency to absorb radiated heat, while utilizing the original as an intermediate means for transferring, from a carrier of a coating of a fusible copy printing dye composition, selected spots of said composition to each of a number of copy receiving sheets, said apparatus comprising, in combination, a rotary drum arranged to start and stop rotating in a substantially predetermined angular position and having an external envelope wall divided into a first circumferentially extending surface part (2A) adapted to serve as a support for the original and havIng means for detachable mounting the same thereon, and a second circumferentially extending surface part (2B) separated from said first surface part in a manner to substantially prevent the transmission of heat thereto, when said second surface part is subjected to heat radiation; a radiation source unit (9,10) capable of delivering a concentrated radiation rich in infrared rays towards the drum, said unit being mounted outside the drum in a manner to irradiate said second surface part thereof, when the drum is at standstill in its start and stop position, and to form a radiation zone of high intensity and limited width extending axially along the drum so as to be passed by the original with the radiation absorbent picture thereon, when the drum is rotated; a movable web-like carrier of a thin coating of the fusible dye composition; conducting means for temporarily bringing said carrier web into intimate contact with the drum-mounted original at a location behind the radiation zone formed by said radiation source unit, as viewed in the direction of rotation of the drum, and including a conducting roller arranged to be alternately moved towards the drum, when first surface part thereof carrying the original is passing, and away from the drum, when said second surface part thereof is passing; and feeding means for bringing copy receiving sheets into intimate contact with said drum-mounted original at a location behind that, where said conducting roller is located, as viewed in the direction of rotation of the drum, said feeding means including a pressure roller adapted to press each copy receiving sheet against the original and means for separating each such sheet with the copy imprint thereon from the drum-mounted original before the latter is again caused to pass the radiation zone formed by said radiation source unit.
 2. An apparatus according to claim 1, wherein said first surface part (2A) of the drum is formed on a wall portion thereof having heat insulating properties.
 3. An apparatus according to claim 1, wherein said first surface part of the drum has a heat insulating covering, at least under the original.
 4. An apparatus according to claim 1, wherein said first surface part of the drum has heat repellent properties.
 5. An apparatus according to claim 1, wherein said second surface part (2B) of the drum has radiation reflecting properties.
 6. An apparatus according to claim 1, wherein said coated carrier web is arranged to start running over said conducting roller already before coming into contact with the drum-mounted original, when said conducting roller is moved towards the drum, and to cease running, when said conducting roller is moved away from the drum.
 7. An apparatus according to claim 1, wherein said coated carrier web is transferred between two spools when running over said conducting roller, said spools being incorporated together with the conducting roller in a detachable, reversible and substantially symmetrical magazine unit forming part of the apparatus.
 8. An apparatus according to claim 7, wherein said spools included in the detachable magazine unit are arranged, when said unit is being inserted, to be connected with each one of two slip friction clutches, the one of which is adapted to transmit a braking power and the other one a driving power to their related spools and hence to the coated carrier web running between them.
 9. An apparatus according to claim 1, wherein said pressure roller forming part of the feeding means for the copy receiving sheets is arranged to be pressed towards the drum only when said first surface part thereof is passing, and to be departed from the drum at least when said second surface part thereof is passing.
 10. An apparatus according to claim 1, wherein a second radiation source unit (43,44) capable of delivering a concentrated radiation rich in infrared rays is mounted outside the drum in a manner to irridiate said second surface part thereof, when the drum is at standstill in its start anD stop position, and to form a second radiation zone of high intensity and limited width extending axially along the drum at a location to be passed by the drum-mounted original shortly before the latter arrives to said pressure roller, where it is brought into contact with the copy receiving sheet.
 11. An apparatus according to claim 10, wherein said second radiation source unit is arranged to irradiate the passing original in an obliquely forward direction, as viewed in the direction of rotation of the drum.
 12. An apparatus according to claim 10, wherein said second radiation source unit and said pressure roller forming part of the feeding means for the copy receiving sheets are so located in the apparatus that the drum-mounted original, when the drum is started, will have to pass them both before arriving to said first radiation source unit and said conducting roller for the coated carrier web, both said first and second radiation source units being positioned below the axis of the drum. 